Most analytical techniques used in industry include taking samples to the laboratory to be analyzed by time consuming procedures. For use in the field, e.g., on-site analysis, spectral analyzers have been gaining favor because of the potential speed of analysis and the fact that they often represent a non-destructive means of analyzing samples. Based on spectroscopy technology, it is possible not only to determine the characteristics of a sample surface, but often the constituent components beneath a sample surface.
Typically, in spectroscopic applications an optimal range of wavelengths is selected to irradiate a sample, where reflected or transmitted light is measured to determine the characteristics of the sample. Some samples, for example, are best analyzed using a near infrared spectrum of light while others are optimally analyzed using a range such as visible or mid infrared spectrum.
Many spectral analyzers utilize a narrow spot size to intensely irradiate a sample to be analyzed. Illuminating a sample with a highly intense incident light typically results in an easier collection of larger amounts of reflected light, thus improving system performance. Unfortunately, a narrow spot size can sometimes provide inaccurate measurements because a small spot may not be representative of the intended sample, particularly where the sample is heterogeneous in nature, such as, for example, grains, seeds, powders or and other particulate or suspended analytes. A narrow spot may unduly heat the sample, affecting the nature of the spectra.
The present invention relates to spectral analysis systems and methods for determining physical and chemical properties of a sample by measuring the optical characteristics of its transmitted and/or reflected light. In general, the systems and methods of the present invention are useful for examining the spectroscopic characteristics of materials, such as particles or liquids, though the systems may be used to characterize other materials such as suspensions of particles and even gases. In certain embodiments, the subject system may be used in connection with non-uniform material, e.g. consisting of components of different compositions, because the system of the present invention does not require the samples to be homogeneous in order to achieve reliable results.
However, in addition to characterizing heterogeneous materials, the subject systems can also be used to ascertain whether or when a mixture or a stream of material is sufficiently homogeneous or fulfils certain specifications with regard to content and/or particle size.
One aspect of the invention relates to a probe head for spectroscopic analysis of a sample material that minimizes the effects of surface reflection on the spectral analysis of the sample thereby improving the spectral analysis. In such embodiments, the invention provides a probe system for spectral analysis in industrial, drug manufacturing, chemical and petrochemical settings and the like. In one particular embodiment, the probe is used in situations with sample materials having a large component of surface reflections relative to light paths passing through particles or a bulk of sample material in a diffuse, scattering path.
In particular, the invention provides a probe head for use with a spectrometer to analyze a material, the probe head having: (i) a light source arranged to irradiate a sample volume of the material proximate the probe head, which source may be a lamp or other radiation source disposed in the probe head, (ii) an optical pick-up, arranged to receive light energy reflected or otherwise emitted from the sample in the irradiated sample volume and transmit the emitted light to the spectrometer for analysis, (iii) an optical blocking element positioned within the optical path between the light source and the optical pick-up to force the optical path into the sample volume, and (iv) a reference shutter for selectively blocking light emitted from the irradiated sample volume from reaching the optical pick-up to facilitate calibration. The optical blocking element can minimize direct surface reflections from the sample or from components of the probe head, such as, for example, a sample window positioned in contact with or proximate the material, relative to light passing through and reflecting from the material within the sample volume to thereby improve the accuracy of the analysis of the material. The light source may provide a suitably broad bandwidth of light for irradiating the sample, and in certain preferred embodiments, simultaneously with multiple radiation wavelengths. The light pick-up receives light reflected or emitted from a sample being irradiated, and is in optical communication with one or more detectors which measure the intensity of the reflected light, e.g., in a wavelength-dependent manner. The detector may be located distal to the probe head and the pick-up may be an aperture in the probe head connected with an optical fiber or other waveguide that communicates light reflected or emitted by the sample to the detector. Alternatively, the detector may be proximal to the irradiated sample, e.g., within the probe head, and the pick-up may simply be an aperture for permitting light being reflected by the sample to enter the probe head. The spectrometer may include one or more signal processing circuits, such as in the form of a computation subsystem, for processing signals outputted from the detector.
In one embodiment, a method of performing spectral analysis comprises the steps of irradiating a sample volume of the material with light from a light source, transmitting light emitted from the irradiated sample volume to an optical pick up that is optically connected to a spectrometer, forcing an optical path between the light source and the optical pick-up into the sample volume, and selectively blocking light emitted from the irradiated sample volume from reaching the optical pick-up to facilitate calibration of the spectrometer. The step of forcing the optical path may include blocking light reflected from a sample window within the optical path from reaching the optical pick-up. The step of selectively blocking light may include selectively moving a reference shutter into the optical path to block light emitted from the irradiated sample volume from reaching the optical pick-up.
Another aspect of the invention relates to a probe head for use with a spectrometer to analyze a material. The probe head may comprise a housing having a first chamber separated from a second chamber, a light source disposed in the first chamber and arranged to irradiate a sample volume of the material with a plurality of wavelengths of light, a wavelength separator disposed in the second chamber, the wavelength separator receiving light reflected from the irradiated sample volume to produce spatially separated light of different wavelengths, and a detector connected to the spectrometer. The detector is preferably disposed in the second chamber and positioned to receive the spatially separated light from the wavelength separator. The detector operates to transmit a signal to the spectrometer representative of the intensity of the spatially separated light received from the wavelength separator.
The first chamber of the housing may include a first window and the light source irradiates light through the first window onto a sample volume. Additionally, the second chamber of the housing may include a second window and the wavelength separator receives light through the second window from the irradiated sample volume. A reflector may be positioned in the housing to reflect a portion of light emanating from the light source into the second chamber for calibration measurements. The probe head also may include a reference shutter for selectively blocking light emitted from the irradiated sample volume from reaching the detector to facilitate calibration of the spectrometer and a diffuser for diffusing light reflected from the irradiated sample volume into the wavelength separator.
In certain embodiments the detector of the probe head may have a larger viewing aperture, for example, greater than about 0.5 square inches and, preferably, between about 0.5 square inches and about 10 square inches. Additionally, in certain embodiments, the light source may illuminate a larger spot size, for example, greater than about 0.5 square inches, and preferably, between about 0.5 square inches and about 10 square inches.
Another aspect of the invention relates to a probe head for use with a spectrometer that facilitates the spectral analysis of a material flowing in a sample containment apparatus, such as, for example, grain or other agricultural product flowing in a duct. The probe preferably includes a housing that is configured for positioning on a sample containment apparatus to monitor a material flowing through the sample containment apparatus.
As will be understood, there are a wide variety of materials for which the systems and methods of the present invention can be used for characterization. Without intending to be limiting, exemplary materials include:
vegetable foods, such a wheat, corn, rye, oats, barley, soybeans, amaranth, triticale, and other grains, rice, coffee and cocoa, which may be in the form of whole grains or beans, or a ground or comminuted product (analysis for protein, starch, carbohydrate and/or water), seeds, e.g. peas and beans, such as soybeans (analysis for protein, fats and/or water), products mainly consisting of or extracted from vegetable raw materials, such as snacks, dough, vegetable mixtures, margarine, edible oils, fibre products, chocolate, sugar, syrup, lozenges and dried coffee extract (powder/granulate),
animal foodstuffs, such as dairy produce, e.g. milk, yogurt and other soured milk products, ice cream, cheese (analysis for protein, carbohydrate, lactose, fat and/or water), meat products, e.g. meat of pork, beef, mutton, poultry and fish in the form of minced or emulgated products (analysis for protein, fat, water and/or salts) and eggs, which foodstuffs may be present in a completely or partly frozen condition,
fermentation broths, such as alcoholic beverages, e.g. wine or beer, fodder, e.g. pellets or dry/wet fodder mixtures of vegetable products, fats and protein-containing raw materials, including pet food,
manure and compost, including composting garbage, grass clippings,
pharmaceutical products, such as tablets, mixtures, powders, creams and ointments,
biological samples including, for example, biological fluids such as blood, urine, spinal fluid, saliva, etc, and tissue samples, and
technical substances, e.g. wet and dry mixtures of cement and mortar, plastics, e.g. in granular form, mineral materials, such as solvents and petrochemical products, e.g. oils, hydrocarbons and asphalt, solutions of organic or inorganic substances, e.g. sugar solutions, glue and epoxies, and
liquids with light scattering properties in suspension, slurries, fluidized materials including both solid and liquid and similar entities.
The components comprising the systems of the present invention are preferably integrated into a single unit, e.g., to create either a portable spectral analyzer or one which is readily disposed along a path of a moving material.